The present invention relates to electrical contacts, and more particularly to electrical contacts which may take the form of ball contacts.
In the past, solder balls have been used for electrical contacts. For example, solder balls have been used to attach semiconductor die to a package or module. Additionally, solder balls have been used to provide electrical contacts from semiconductor device packages to printed wire boards, module level boards, or the outside world. One method for forming the balls has been to pick up preformed solder balls and physically attach them to the desired surface. Solder balls so attached fall off quite easily from forces in the sheer direction and from vibration and acceleration.
Another method that has been employed in the past is to plate the electrical contact material (typically solder) above the surface where the solder ball is to be attached and then reflow the plated solder to form a ball.
A disadvantage of both methods described is that the ball contacts must be formed as one of the last steps of the device manufacturing process. This is because, according to both methods, a ball contact or electroplated solder material protrudes above the surface to which it is attached. Therefore, the surface is no longer flat, so the device being fabricated can not undergo further processes which require a flat surface. For example, most conventional photolithographic processes as well as deposition processes require that the die being processed have substantially flat surfaces, or at least a flat bottom. Therefore, the prior art methods must be performed toward the end of processing.
What is needed is a method for fabricating an electrical contact which may have the form of a ball contact, and which does not easily break or fall off. Furthermore, what is needed is a method for forming an electrical contact which can be performed relatively early in the device processing cycle and is compatible with later processing steps.